A fuel cell which is in a shut down mode can typically have a dangerously high residual voltage level across its anode and cathode electrodes. In order to reduce the output voltage, the anode and cathode flow fields of the fuel cell are inerted or flooded with an inert gas which, in turn, lowers the output voltage level to about zero volts. One drawback with employing inert gas is the added expense of providing and applying such gas whenever the fuel cell is taken off-line or otherwise shut-down. A second drawback is the operator in charge of fuel cell operation may forget to apply the inerting procedure. If the inerting procedure is overlooked, the reactants will cross-over the membrane separating the anode and cathode electrodes to react with one another to form water. As this reaction progresses, the gaseous volume on the anode side will become depleted and will develop a significant vacuum on the anode side of the system. If the system is not sufficiently leak tight, air from the exterior of the power plant will replace the reacted fuel on the anode side and will represent a hazard to the system when it is again started and fuel reaches the air now occupying the anode gas flow passages. A detonation of this combustible mix may ensue causing damage to the fuel cell system and possibly to people in the vicinity of the fuel cell system.
In response to the foregoing, it is an object of the present invention to provide a self-inerting fuel cell system which overcomes the drawbacks and disadvantages of prior fuel cell systems. Other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.